Abstract: In this experiment,the synaptosomal free calcium concentration and synaptosomal membrane protein-bound Ca2+ in various brain regions were measured by using fluorescence indicator Fura-2/AM and Tb3+ respectively.Compared with that of 3-month-old rats,the synaptosomal free calcium concentration significantly increased in hippocampus,cerebral cortex and hypothalamus of 26-month-old rats.Moreover,the synaptosomal membrane protein-bound Ca2+ obviously increased in hippocampus and cerebellum while in the other brain areas examined (cerebral cortex,hypothalamus) decreased significantly.These suggest that the perturbation of normal Ca2+ homeostasis appears to be an important factor correlated with aging.